A thin film magnetic head to be equipped in a magnetic recording system such as a hard disk drive has been widely used in the recent years. In developing the thin film magnetic head, the recording density of a magnetic recording medium such as a hard disk (hereinafter, “recording medium”) has been vastly improved. However, further improvement in performance was still required. As a result, the magnetic recording system was changed from a longitudinal recording system to a perpendicular recording system. The perpendicular recording system has the advantages that a high line recording density can be realized, and that the recording medium after recording is unsusceptible to the influence of thermal fluctuation.
The thin film magnetic head of the perpendicular recording system (hereinafter, “magnetic head”) is provided with a thin film coil generating a magnetic flux, and a magnetic pole extending rearwardly from an air bearing surface (hereinafter, “ABS”), and conducting the magnetic flux to the recording medium. The magnetic head can magnetize a recording medium by generating a magnetic field (a perpendicular magnetic field) to therefore magnetically record information in the recording medium.
FIG. 1 is a sectional view of a magnetic head 100B′ along with a moving direction (+Z-direction) of a recording medium 80′. The recording medium 80′ is on the left side in FIG. 1 and the recording head 100B′ on the right side. An air bearing surface (ABS) is located on the left edge of the recording head 100B′ which faces the recording medium 80′. An arrow line (F′) in FIG. 1 represents a pathway of the magnetic flux which a main magnetic pole layer 55′ (a portion of a magnetic pole layer) generates. The magnetic flux F′ is directed perpendicularly toward the recording medium 80′ from the ABS of the main magnetic pole layer 55′, penetrates a magnetizing layer 81′ of the recording medium 80′, advances in a soft magnetic layer 82′ of the recording medium 80′ toward a moving direction of the recording medium 80′ (+Z-direction), and returns in a diffused state to the magnetic shield layer 60′ (with a low magnetic flux density). The surface on which the magnetic flux returns is a magnetic shield surface 60M′.
In order to enhance recording density, magnetic distribution and magnetic density by which a transition of bits of recording data becomes clear are required, as well as narrow writing width, with respect to the +Z-direction in FIG. 1. In order to realize the narrow writing width, a strong magnetic field is required even when a width of the main magnetic pole layer 55′ is narrow. Additionally, in order to more completely clear the transition of bits, the following two elements are required:
i) the capability to rapidly switch magnetizing conditions (positive and negative) according to the switching action of the magnetic field (a large magnetic gradient); and
ii) the capability to sufficiently weaken the returning magnetic flux F′ in order not to negatively affect the magnetizing layer 81′ that has been recorded as the flux F′ returns from the soft magnetic layer 82′ to the magnetic shield layer 60′.
When the magnetic field intensity on the ABS of the magnetic shield layer 60′ is significantly large, leakage of the magnetic flux to its surroundings also becomes large. Eventually, such magnetic flux leakage affects the recording medium 80′ negatively. Therefore, it is necessary to keep the magnetic field intensity for recording as small as possible so that there is no magnetic flux leakage. Especially, in view of a demand of higher density of recording data, when the soft magnetic layer 82′ becomes thinner, a magnetic flux in the soft magnetic layer 82′ will be easily saturated. As a result, the magnetic flux overflowed from the soft magnetic layer 82′ converges around the magnetic shield layer 60′ (a bottom edge of the magnetic shield layer 60′). Further, it is also observed that the magnetic flux returns not only at the center but at other areas with a certain distance in the side direction as well. The magnetic flux returned at the sides creates a WATE (Wide Area Track Eraser/Erasing) which is a drawback in erasing written data. It is depicted in FIG. 8 that WATE occurs at lower edges of magnetic field surface 60M on the ABS and at an area having width (φ) from the center line CL in the side direction (X-direction).
What is needed then is a system and structure that prevents a partial concentration of magnetic flux on the magnetic field surface 60M′ by diffusing the return flux in a proper way, and especially prevents the occurrence of WATE.
Prior references describing a technology to prevent a magnetic flux concentration are following:    Ref. 1: U.S. Pat. No. 7,268,974    Ref. 2: U.S. Pat. No. 6,646,828
(Ref. 1)
Ref. 1 (U.S. Pat. No. 7,268,974) discloses a notch (notch 106′) which is located in the magnetic shield layer 60′ and the ABS, further, located on the trailing side from the main magnetic pole layer 55 (see FIG. 7). The notch 106′ is filled with non-magnetic material so that the notch 106′ functions to block magnetic flux. This configuration weakens a magnetic field on the notch 106′, and diffuses the returning magnetic flux in the X-direction. However, the notch 106′ filled with non-magnetic material completely blocks the returning magnetic flux. Therefore, the magnetic flux diffused in the X-direction easily concentrates at both edges of the notch 106′ (shown as ED in FIG. 7). Accordingly, such a configuration described in Ref. 1 still has a drawback that the returning magnetic flux(s) is intently concentrated and enlarged at the edges of the notch 106′.
(Ref. 2)
Ref 2 (U.S. Pat. No. 6,646,828) discloses a configuration disposing a non-magnetic portion in a pathway of a circulation of a magnetic flux in order to prevent a concentration of the magnetic flux. However, this configuration is directed to a longitudinal magnetic recording head which was previously used. Therefore, the basic configuration differs from that of a perpendicular magnetic recording head to which the present invention is directed. For example, an area of a magnetic pole surface on the ABS is completely different in size from an area of a magnetic shield surface, the magnetic pole surface functioning to emit a magnetic flux, the magnetic shield surface functioning to collect the magnetic flux. In the longitudinal magnetic recording head, the magnetic shield surface is smaller than the magnetic pole surface so that data/information is to be recoded when the magnetic flux is in the returning pathway. On the other hand, in the perpendicular magnetic recording head, magnetic shield surface is 100 times or more as large as the magnetic pole surface so that data/information is to be recorded when the magnetic flux is in the outgoing pathway.
(Other Related References)
Other related references describing technologies for moderating the concentrating flux include:    Ref. 3: US Patent Application Publication No. US 2006/0103977    Ref. 4: U.S. Pat. No. 7,196,871    Ref 5: U.S. Pat. No. 7,126,790    Ref 6: U.S. Pat. No. 4,656,546
Further, in order to moderate the strength of a magnetic flux which is collected on the ABS, it is possible to adapt a material having a low saturation flux density in the magnetic shield layer. However, such a configuration possibly deteriorates magnetic coupling with the magnetic shield layer and the magnetic pole layer. Therefore, it weakens the strength of the circulating flux in the recording head, eventually leading to a weakened magnetic flux intensity for writing/recording. As discussed above, these related references still exhibit two drawbacks. One is the prevention of a partial concentration of magnetic flux on the magnetic shield surface. At the same time, the second is the maintenance of a high magnetic coupling between the magnetic shield layer and the magnetic pole layer.